Waxing (and Waning) lyrical on hiatuses: Eocene ‐ Quaternary Indian Ocean hiatuses as proxy indicators of water mass production

Abstract

The temporal distributions of Cenozoic hiatuses in the Indian Ocean are reconsidered in the light of a new time framework developed by the Paleoceanographic Indian Ocean Synthesis. On the basis of the temporal distribution of hiatus terminations, eight 3 m.y. time slices were selected for plotting the paleogeographical distribution of hiatus terminations. These distributions define areas of potential hiatus development, which formed along flow paths of proto‐Antarctic Bottom Water (an analogue of modern Antarctic Bottom Water) and proto‐Antarctic Intermediate Water (an analogue of modern Antarctic Intermediate Water). Expansion and contraction of these areas suggested changes in the volume of these water masses, which modified the distibution patterns of erosive deepwater currents and corrosive bottom water. Consequently, the spatial and bathymetric distribution of hiatus formation was altered. Age‐depth analysis of hiatuses from sites within post‐late Eocene areas of potential hiatus development was used, in conjunction with models of the behavior of unconformity boundaries within fluctuating water masses, to construct waxing/waning curves for proto‐Antarctic Bottom Water and proto‐Antarctic Intermediate Water. These curves define volume changes in the production histories of these water masses which were related to the post‐late Eocene glacial history of Antarctica. Since the late Oligocene, the proto‐Antarctic Bottom Water waned during intervals of increased glacial intensity, whereas the proto‐Antarctic Intermediate Water waxed during these intervals. These relationships reversed during intervals of reduced glacial intensity, including intervals where there is no evidence for Antarctic glaciation. This conflicts with interpretations made by other workers. A comparison is made between the production histories of proto‐Antarctric Bottom Water and Northern Component Water (an analogue of North Atlantic Deep Water) based on ∂13C for the Miocene to Pliocene.